The breeding cycle in female pigs

Most gilts (young females) show their first oestrus between 170-220 days old, which is usually around 90kg liveweight.

Age and not weight limit puberty in modern strains of fast growing pigs fed high energy diets.

Puberty can also be affected by breed, season of the year and social contact (stocking density).

Mixing gilts during transport can also stimulate onset of first oestrus (heat).

Contact with male pigs can also stimulate first heat. This “male effect” works best when young females are kept separate from the boar then the boar is introduced when the femails are 160-175 days old. Prolonged exposure to the male will not trigger heat.

This “male effect” does not work with gilts reared with their boar littermates.

In commercial practice, gilts are mated at their third heat when they weigh around 118kg liveweight. But they can be mated at their second heat if intensive production is the objective.

Females cycle at intervals of about 21 days (range18-24).

Signs of heat:

Swollen and red vulva 2-6 days before oestrus.

Mucous discharge from vulva.

Prick-ear breeds hold their ears erect and pointing backwards.

Restless and poor appetite.

Sniffing genital area and riding pen mates.

When at peak oestrus they show the “stance reflex” by arching their back, stand rigidly when pushed from behind, and allow you to sit on their backs.

They make a characteristic squeaky grunt and seek out other pigs as they look for a boar.

Standing heat when the female accepts service lasts for about 48 hours (range 38-60 hours). Some sows may stay on heat for 120 hours.

First heat is usually shorter than later ones, and sows have longer receptive periods than gilts.

Length of oestrus varies between breeds and is affected by season and management system.

Ovulation occurs during the second half of the heat period so it’s a good idea to serve females twice, at the start and the end of standing heat.

Ovulation in females is strongly affected by boar pheromones in the boar odour.

Breeding females come into heat usually within 7 days of traditional weaning of the litter. So to get more litters per year, early weaning has become general practice. A good commercial target is 1.5 litters/year.

Gilts after their first litter will return to heat a few days later than older sows that have had many litters.

The rebreeding period of sows can be shortened by high feeding levels (flushing) and lengthened by stress (eg fighting when put into groups).